Question

an object is seen to either speed up, slow down, or change direction. what are these behaviors are caused by? a balanced set of forces unbalanced forces stable factors frictional force

Explanation:

According to Newton's first law of motion, an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. When an object speeds up (accelerates), slows down (decelerates), or changes direction, its velocity (which is a vector quantity - has both magnitude and direction) changes. A change in velocity is acceleration. Unbalanced forces cause acceleration. Balanced forces result in no change in motion (constant velocity or at rest). Stable factors is a rather vague term not related to the cause of motion changes in the context of physics laws. Frictional force is a type of force, but it's unbalanced forces in general (could be friction or other forces like applied force etc.) that cause the described motion changes.

Answer:

unbalanced forces